This invention relates to an artificial joint intended, in particular, as an endoprosthesis for the human knee joint, comprising a first joint compartment formed by a first condyle and a first socket and a second joint compartment formed by a second condyle and a second socket. Contact surfaces of the respective joint compartments are offset in the main functional plane.
Published German patent application no. DE 39 08 958 A1 discloses an artificial joint intended to replace a human joint, which is made of two joint components with mobile functional surfaces. The curvature relationships of the functional surfaces having a circular cross-sectional contour are mutually convex-convex, convex-concave or concave-concave, and the joint geometry is determined by a joint chain with two joint axes (dimeric joint chain), which pass through the centers of rotation of the functional surfaces. The joint surfaces are spherical to enable the joint to move with five degrees of freedom.
Published European patent application no. EP 734,700 also discloses an artificial joint in which the joint geometry of the functional surfaces relative to one another is determined by a joint chain with two joint axes in each of the two planes. The joint axes pass through the centers of rotation of the functional surfaces with the radii of the respectively associated cross-sectional contours. A femur-side, i.e., a condyle-side, connection of the center points of the condyles corresponds to a frame and a tibia-side, i.e., a socket-side, connection of the center points of the sockets corresponds to a coupling of a four-bar linkage having the four axes. This makes it possible, in particular, in the flexion area of the joint between 0 and 30°, to obtain a high rolling component in the contact of the joint surfaces. The contact surfaces initially move in posterior direction relative to the socket. With further flexion, a sliding movement occurs without any shifting of the contact surface. As a result, the condyle cannot roll out of the socket.